We investigated electrofishing catchability (q) for brown trout Salmo trutta and rainbow trout Oncorhynchus mykiss in the Colorado River, Grand Canyon National Park, Arizona, over a range of fish densities, water temperatures, turbidities, conductivities, shoreline types, and seasons. The covariance of q with rainbow trout density strongly resembled random distributions, thereby suggesting no relationship between q and rainbow trout density. The catchability of rainbow trout was greater in turbid water (?480 nephelometric turbidity units [NTU]) than in clear water (?10 NTU), although lower water temperature may have contributed to this effect. The catchability of rainbow trout was greatest over sand?silt shorelines. The catchability [...]